USB Core Audio Problem with Max/MSP 5.1.2

I had a mysterious dumbfounding experience with Max 5.1.2 and the USB Core Audio drive over the weekend. I was sending audio from Max to a Numark C3 USB mixer (Mac Book Pro OS 2.5.8, 2.16 Intel Core Duo, 2 GB Ram) and the sound was incredibly hissy and noisy. If I played the same audio from the Apple Quicktime Player it sounded just fine. I’ve used the exact same set-up a lot with Max 4.6 and never experienced any sound quality problems. Is this a Max/MSP 5 bug? Or are there peculiar settings I’m not aware of in Max 5 that I need to set for the sound to play without hiss and crackle. Would upgrading my operating system to Snow Leopard solve the problem? I tested a Presonus Firebox and that sounded just great but one of the reasons I got this mixer was to be able to hook to laptops up via USB and reduce the amount of gear I have to travel with. Any help/advice with this will be sincerely appreciated.